The present invention relates to multi-roll leveling apparatuses for leveling metal strip material and, more particularly, to leveling apparatuses in which the penetration of the work rolls may be varied along the lengths of the work rolls.
During the process of manufacturing coils of metal strip materials such as steel, aluminum, brass and the like, variables in the process cause lack of flatness in the finished strip. The term "lack of flatness" is used to denote the deviation in the strip material from a planar configuration when uncoiled and allowed to lie flat.
For example, a rolling process in which the longitudinal edges of the strip are elongated more than the center of the strip results in a strip having wavy edges. The wavy edges accommodate the excess in length of that portion of the strip adjacent its edges. Conversely, a rolling process in which the center of the strip is elongated more than the edges results in a strip having centrally-located buckles or bubbles.
The process of working the strip to remove waves, buckles, and other deviations from a planar shape is known as "leveling", and it involves the selective elongation of the strip such that the same amount of material exists per unit length across the width of the strip. There are numerous devices for performing this elongation operation. With many of these devices the elongation is caused by passing the strip between a series of upper and lower work rolls which are offset from each other and are somewhat nested. As the strip of metal to be leveled is passed between these two sets of rolls it follows a serpentine path, flexing as it passes about the circumference of each of the work rolls.
Each of the flexes or bends about the outer surface of a work roll causes the portion of the sheet most distant from the center of curvature to be elongated, while the portion nearest the center of curvature is somewhat compressed. Successive elongations and compressions of the strip in this manner result in a strip which is substantially uniformly elongated across its width and therefore possesses the requisite flatness.
The upper and lower work rolls are positioned so that the degree of penetration or nesting decreases from the entry rolls to the exit rolls, so that the amount of flexing decreases from the front to the rear of the leveling apparatus. The final flexing of the sheet by the exit work rolls is just sufficient to return the material to a flat, planar condition.
However, sheet material frequently comprises a combination of wavy edges, center buckles and other deviations from flatness across its width so that it is necessary to vary the penetration of the work rolls along their lengths. For example, it would be necessary to increase the amount of flexing in the vicinity of the center of a sheet in order to elongate that portion and remove wavy edges on that sheet. Conversely, a center buckle appearing in a sheet would be removed by increasing the penetration of those portions of the work rolls contacting the edges of the strip, so that the edges are elongated sufficiently to correspond to the length of the center of the strip.
Another defect appearing in metal strip coils is longitudinal and transverse curvature. Longitudinal curvature occurs when one surface of the strip is longer than the opposite surface in a lengthwise direction; while transverse curvature occurs when one surface is longer than the opposite surface in a transverse direction. In contrast to the type of working required to remove wavy edges and center buckles, the removal of longitudinal and transverse curvature is accomplished by increasing the penetration of the work rolls uniformly along their lengths. Therefore, two different types of metal working are required to produce a flat strip having both longitudinal and transverse curvature as well as wavy edges and/or center buckles.
Several types of leveling apparatuses have been developed with the object of providing adjustable work rolls which remove both types of defects in a single pass. For example, the Bearer U.S. Pat. No. 3,301,031 shows a leveling apparatus in which both the upper and lower sets of work rolls are supported along their lengths by a plurality of back-up roller assemblies. Each roller assembly rests upon a pair of wedges which are adjustable to urge the roller assembly upwardly to deflect the portion of the work roll it supports, and thereby vary the penetration of the upper and lower work rolls at that location. The wedges can be positioned so that the back-up rollers urge the entry work rolls toward the strip material a greater distance than the exit work rolls are displaced, thereby varying the penetration of the work rolls along the length of the leveling apparatus.
Similarly, the Krynytzky U.S. Pat. No. 2,963,071 shows a leveling apparatus which includes a plurality of individually adjustable back-up rollers which are spaced along the lengths of the work rolls. Each back-up roller includes a support member having semicircular cavities at its front and rear portions, and the frames which support the support members include a pair of semicircular blocks which matingly engage the cavities. The blocks contact upon longitudinally-adjustable wedges so that the entry or exit portion of the support member may be adjusted to vary the elevation of the back-up rolls and therefore vary the penetration of the work rolls supported by those back-up rollers. As the wedges are displaced, the blocks pivot relative to the frames.
A disadvantage inherent in both of the aforementioned leveling devices is that it is difficult to adjust the deflection of the work rolls to correct for one type of defect in a metal strip, such as longitudinal or transverse curvature, without affecting the ability of the work rolls to correct another type of defect, such as wavy edges or center buckles. This results from the difficulty in varying the penetration of the work rolls along their lengths without varying the average penetration of the work rolls along the path traveled by the metal strip. Accordingly, there is a need for a leveling apparatus which may be adjusted to correct for wavy edges and center buckles on a strip without affecting the overall penetration of the work rolls in removing the longitudinal or transverse curvature of a strip.